1. Field of the Invention
The present invention relates to the structure of an electrode used for electrical discharge machining which is employed for an electrical discharge machine that machines a workpiece by the action of electric discharge and, more particularly, to an electrode capable of machining parts having intricate shapes by electrical discharge machining.
2. Description of the Related Arts
Conventional methods of intricately spark-machining workpieces include a method utilizing photolithography adapted to machine semiconductors, a method using an LIGA process, and a method of machining a workpiece into a desired shape by electrical discharge machining. In the method using the LIGA process, a photosensitive material is molded, using synchrotron radiation. Then, the material is plated with a metal. Thus, the material is machined into a desired shape.
The electrical discharge machining which is also known as electron discharge machining, electric spark machining, electroerosive machining, and electrospark machining is described now. The following three kinds of electrodes can be employed for electrical discharge machining.
A first kind of electrode is an electrode 20 shown in FIG. 11. This electrode 20 takes the form of a flat plate and is provided with a plurality of holes 20a. A workpiece 21 is mounted opposite to the electrode 20. A power supply 22 for electrical discharge machining applies a voltage, which produces an electric discharge from the flat-plate electrode 20 to thereby machine the workpiece 21.
A second kind of electrode is a single needlelike electrode 23 shown in FIG. 13. A voltage is applied between the electrode 23 and a workpiece 21 to create an electric discharge. Utilizing this discharge, holes are formed in the workpiece 21. Since the area of the front end of the electrode 23 is much smaller than the area of the flat-plate electrode 20, the energy of a single electric discharge is small. Hence, the machining accuracy can be enhanced.
A third kind of electrode is a wire electrode 24 shown in FIG. 14. A voltage is applied between the wire electrode 24 and a workpiece 21. At the same time, the workpiece 21 is rotated. In this manner, the workpiece is machined into a needlelike shape. During the machining, the wire electrode 24 is fed in to suppress the wear of the electrode due to the electric discharge. Also, the machining accuracy can be improved.
However, where a workpiece 21 is machined so as to leave minute regions, or minute cylindrical portions 21a, as shown in FIG. 12 by the prior art machining techniques, various difficulties arise.
In the method using photolithographical techniques principally relying on etching used to machine semiconductors, if the height of the cylindrical portions 21a shown in FIG. 12 reaches tens of microns, lateral etching also occurs, thus deteriorating the dimensional accuracy.
In the LIGA process, the cost is very high because of the use of synchrotron radiation.
Furthermore, in the prior art method making use of electrical discharge machining, the machining accuracy and the machining time present problems. The problems with the above-described electrode structures are described next.
Where the flat-plate electrode 20 shown in FIG. 11 is used, the area of the electrode is large and so the energy produced by a single electric discharge is large. Therefore, the outer surfaces of the cylindrical portions 21a formed by the holes 20a tend to be uneven. Consequently, it cannot be anticipated that high machining accuracy is obtained.
Where the single needlelike electrode 23 shown in FIG. 13 is used, it may be possible to enhance the accuracy at which the cylindrical portions 21a shown in FIG. 12 are machined, by scanning the electrode 23 or the workpiece 21. However, the machining time is increased. Furthermore, a mechanism for scanning the electrode 23 or the workpiece 21 is needed. Also, measures must be taken against the wear of the electrode 23.
Where the wire electrode 24 shown in FIG. 14 is employed, the wear of the electrode can be suppressed but the machining time is prolonged. Also, a mechanism for scanning the electrode or the workpiece is needed. In addition, the machining accuracy is lower than the machining accuracy obtained where the needlelike electrode 23 is used, because the electric-discharge area at the front end of the wire electrode is wider than the electric-discharge area of the needlelike electrode 23.